This invention relates to a method for manufacturing a composite material, in particular a ceramics or the like containing composite material, as well as to a composite material.
The use of ceramics in applications where conventionally metals were used has recently increased markedly. Reasons for this are, for instance, various clearly improved material properties, such as wear-resistance, hardness, corrosion-resistance, modulus of elasticity, dimensional stability, chemical resistance and heat-resistance. One of the important disadvantages of the use of ceramic materials, however, is that they are relatively brittle. Further, their resistance to thermal shocks is poor. Moreover, good ceramic composites are relatively expensive. As a consequence, the possible areas of application of ceramic composites are limited.
In order to avoid these disadvantages, a number of proposals have been made for the manufacture of such composites with improved properties.
European patent application 0,378,500 describes a method for manufacturing a metal-infiltrated composite material which comprises reaction products of the metal with boron and/or carbon To that end, from a boron donor material and a carbon donor material, a self-supporting intermediate of a relatively high porosity is formed, whereby bonds between the material particles are effected, for instance during sintering of the intermediate. Thereafter the intermediate is contacted with a molten parent metal, in a manner and for a time suitable to obtain a reactive infiltration. The space existing between the mutually bonded particles is thereby filled with the metal and the whole is maintained at a suitable temperature for a suitable time, in such a manner that at least chemical bonds are formed between boron and metal, carbon and metal and boron, and/or carbon and metal. As a result of the reactive infiltration, a composite material is formed with mutually bonded particles with residual metal between them.
In this method, bonds between the different particles are effected, partly prior to the infiltration. As a result, a base product with a relatively high density and relatively coarse particles is formed, whereby the product does not acquire a completely open porous network. Any closed porosity present in the product is not removed and therefore not filled with metal during the infiltration. The particles are not entirely surrounded by the metal, so that no fully continuous matrix is obtained in which the particles are embedded. Moreover, the properties of the starting materials change considerably as a result of the chemical reactions.
U.S. Pat. No. 4,879,262 describes a method for manufacturing composites and in particular boron-containing composites, using combustion synthesis of boride compounds and composites. To that end, a suitable mixture of at least a first, B.sub.4 C rich component and a second, B.sub.4 C/TiB.sub.2 rich component is composed and heated such that a maximum inclusion of the relatively light B.sub.4 C into the relatively heavy B.sub.4 C/TiB.sub.2 is obtained, whereafter a self-sustaining combustion is effected in the mixture, such that a densification of the matrix arises as a result of the chemical reaction. The densification is not maximal, so that a porous structure is left. Thereafter the porous composite obtained is infiltrated with liquid metal, for instance aluminum. As a result, a composite of a relatively high density is formed. It is noted that in this way other composites can also be obtained, provided a self-sustaining combustion front can be generated therein.
This method can only be used with specific combinations of starting materials, while moreover heating prior to the combustion is required in order to obtain a good densification. Further, a relatively coarse division of the particles is obtained, while the particles will frequently be in mutual abutment. Any porosity present, which may or may not have arisen during the reaction, is not prevented, reduced or removed in this known method. No completely open porous network is formed, so that the particles cannot be completely surrounded by the metal. Moreover, as a result of chemical reactions that occur, the properties of the starting materials change.
European patent application 0,207,371 describes a method for manufacturing composites, in which powders are dynamically densified to a very high relative density. The shock induced by an explosive and/or strike plate in this method should be so high that exothermic sintering of the powders occurs. Chemical bonds and possibly plastic bonds between the powder particles are thereby formed, so that a closed network is obtained of, for instance, metals, oxides and the like, and a substantially full density.
In this method a very strong shock should be induced, in such a manner that the starting powders enter into an exothermic chemical reaction. As a result, the composition, and hence the chemical and mechanical properties, of the mixture changes. Moreover, a continuous network of ceramic particles fixedly bonded to each other is obtained, which particles are therefore not embedded in another material which forms a continuous matrix. As a result, the material obtained does not have an optimum resistance to, for instance, thermal shocks and it is insufficiently tough. Moreover, only starting powders capable of entering into the desired exothermic reactions with each other can be used.